The research described in this proposal will; (1) provide a better understanding of the development of homeostatic regulation, specifically water regulation, (2) increase our knowledge of the effects of infant brain damage and recovery (or lack of recovery) of function, and (3) advance our understanding of the early and late regulatory effects of infant undernutrition. Three basic experiments are described; the first concerned with the age at which cellular and extracellular stimulation effects the drinking response, the second concerned with determining the effects of selected neural destruction of infant rats on the develpment of water regulation, and the third concerned with more specific analysis (single neuron recording) of those neural areas whose destruction affects the development of water regulatory ability. The first experiment determines when in development cellular dehydration and extracellular hypovolia are effective in stimulating drinking behavior. The second experiment uses the brain lesion technique for determining what neural tissue is involved in the control of water regulation. Effects of lesion locus and age at which damage was sustained will be evaluated in terms of changes in basic metabolic and behavioral phenomena related to water regulation. Those neural areas which, as a function of damage, effect changes in ability to maintain water balance will be subjected to single-unit-recording analysis (Experiment 3). Unit activity will be analyzed for correspondence with various behavioral and physiological correlates of water regulation.